Grinder Bits

Extending the life of your grinder bits is a matter of recognising that you should not force the glass into the grinding head. Excessive pressure against the head heats the bit and allows the diamonds to become free of the binding material, so reducing its life. If the motor slows as you press the glass to the bit, you are applying too much pressure. That kind of pressure also puts a lot of wear on the bearings of the motor.

If the grinder is not taking glass off fast enough for your purposes, you should put a coarser bit on the grinder, rather than pressing harder. The bits do come in a variety of grits. Try out some different grits to find the one that works best for the speed at which you want to remove the glass.

You can also buy a additive for the water – often called a diamond coolant – which is intended to provide a kind of lubrication for the diamonds. This may also extend the life of the bit.

Replacing Grinder Heads

The best action is to prevent difficulties from the start. Before putting the grinder bit onto the shaft, coat it with Vaseline or a proprietary anti seize-compound. This will ease the removal of the bit later.

If the bit is already seized, the method of removal is based on how fast it is stuck. If there is a bit of movement around the shaft when the grub screw is removed, you can probably remove it with simple tools. First use very fine wet and dry sandpaper to remove all corrosion and roughness from the upper, exposed part of the shaft. Put a thin film of lubrication or penetrating oil on the shaft and then you can hold the top of the shaft tight with smooth-jawed pliers while you twist the bit. Be careful not to mark the shaft or you will create another obstacle to removal of the bit. Alternatively, while pulling up on the bit, you can tap the top end of the shaft gently with a plastic hammer to shake the bit loose.

If this does not work, remove the grid and turn the dry grinder upside down and spray WD-40 or other penetrating oil to the bottom of the grinder bit.  This should be left for a few days with renewal of the penetrating oil every half day.  Then try the methods above to free the bit from the shaft.

If the bit is firmly stuck, you will need a small wheel puller to get the bit off the shaft.

Once you have the bit off, smooth any corrosion with fine wet and dry sandpaper and lubricate the shaft. Periodic removal of the bit and lubrication of the shaft will become part of the regular maintenance of the grinder.

Flat Bottoms for Bowls

There are at least three ways to achieve flat bottoms to bowls without the use of external supports.


Using drop out rings will enable you to get a flat bottom of whatever diameter you wish depending on how long you let the aperture drop run.

You can put some dry kiln wash into the bottom of the mould, then firmly press it flat with a round piece of glass. You will need to make sure it is horizontal, so the use of a small round levelling bubble can make this easier.

Grind a flat spot on the bottom of the otherwise finished bowl. It is a good idea to use a two way leveling bubble while grinding. The round bubble is easier to use, while the two way bubbles – two leveling bubbles placed at right angles – are more accurate.

Mesh Sizes from a Typical Manufacturer

Mesh sizes have traditionally been measured by the number of wires per square inch used to sieve the material. This table gives a grit size measurement for the mesh/grit numbers in common use.

Mesh = Mesh opening (mm)
12 =   1.5240
14 =   1.2954
20 =   0.8636
30 =   0.5156
40 =   0.3810
50 =   0.2794
60 =   0.2337
80 =   0.1778
100 = 0.1397
120 = 0.1168
200 = 0.0737
325 = 0.0432
400 = 0.037
625 = 0.020
1200=0.012
2500=0.005

Polishing 3D Glass on a Wet Belt Sander

Polishing three dimensional objects depends on the shape of the glass you are sanding down to the polished surface.

Convex shapes can be done on the wet belt sander with ease.

You can polish slightly concave items on a belt sander if you have an unsupported section of the belt. On machines with a flat platen, you can remove the platen to use the ability of the belt to form into a slightly convex curve.

Glass Polishing Machines - Linisher

A wet belt sander, or linisher, is a machine intended to grind the edges of flat pieces of glass. It can do some work on bent, shaped, or slumped work, but its primary function is edging work while it is flat.

Table top model

The machines consist of a vertical or near vertical belt and a water supply to keep the belt and work lubricated and cool. Work generally starts with a low numbered grit belt, perhaps 80 grit, and then proceeds through the higher numbers. For example: 80, 120, 220, 400, 600, cork. Each stage should approximately half the grit of the previous one.

Floor standing model

Even with a cork belt, don’t expect a gloss you would see from a fire-polished piece. For that you need a cerium oxide belt or a felt belt with cerium oxide paste. Trizact is a brand name for fine polishing belts not requiring cerium oxide paste. These may be substituted for the more messy paste methods.

You can buy silicon carbide or diamond belts for a wet belt sander. The diamond belts are very expensive, but much longer lasting with proper care. If your belts are likely to receive rough treatment stick with the cheaper silicon carbide belts.

Grinding for Copper Foil

It is often thought that every piece of glass has to be ground to enable the foil to stick well to it. There are conflicting views about this. I am firmly on the side of not grinding. The impact adhesive on the back of the foil is thin and will not fill the depressions caused by grinding. It will adhere to a smooth surface more strongly than a rough one. Remember the purpose of the foil is to provide a surface to carry the solder. It keeps the foil in place until the solder bead is completed on both sides. It is not a permanent adhesive. So some of the discussion about which surface is best is academic.

There are ways of obtaining clean cuts that help avoid the need to grind.

Score with an even pressure. This helps the glass break clean with few shells or chips. If there are any overhangs, you can eliminate them with a quick wipe of the edge of the cut piece on the waste piece.

Ensure you hold your cutter vertically. This will encourage the break to be at right angles to the surface giving a clean smooth cut face.


The only NEED for grinding is to adjust an inaccurate cut. We all make inaccurate cuts from time to time.

Water Proofing of Pattern Pieces

Many people put their pattern pieces onto the glass they are going to grind, or saw to attempt to get a good fit to the cartoon. The water from the grinder makes paper templates soggy and liable to tear or disintegrate so failing to for a good guide to grinding.

One solution is to stick self adhesive plastic on top of the pattern before you cut it all apart. Then you have some protection when you grind.  The plastic sticks to the surface of the paper and resists the water.  However, the water can seep between the glass and the unprotected bottom of the paper or, even if protected with plastic on both sided, through the exposed edge.

You can spray or apply clear lacquer on the paper pattern pieces before attaching them to the glass and grinding. This has slightly better results as the edge is most often sealed better than with two layers of plastic.

You can use clear acetate film (ca. 0.2mm thick) as a completely water resistant pattern. Cut your pattern pieces from the acetate film and stick them on to the glass with blutack or any other gum based adhesive. This works well and does not suffer from the water deteriorating the pattern piece.

Finger Protection While Grinding

Various methods of protection are used:
Finger stalls,
Taped fingers,
Altering the fingers used to press the glass to the grinding bit,
Gloves – but they have to very tight fitting to avoid getting caught in the spinning bit.
Duct tape,
Grinders' Mate.

Prevention
The sore fingers are usually caused by tiny cuts from the glass. So, all these methods are ways of putting something between the glass edges and your fingers. More importantly, you need to think about your practice if you are getting sore fingers while grinding.

The first thing is just to lightly grind all the way around the piece first. This can be quick, and should use minimum pressure. This will remove any sharp edges.

If you have to press hard to achieve the effect you want, it may be that your grinder bit is badly worn. It may also be that you need to have a coarser bit to achieve the amount of grinding that you need.

You should not be pressing hard in any case. This will wear out bearings on the motor and reduce the life of the bit. You should use medium pressure and allow the diamonds on the grinding bit to do the work. Fine work requires a fine grit, removing a lot of glass requires a coarse bit, not more pressure.

If you have to remove large amounts of glass, you need to review the accuracy of your cutting. You should not be relying on the grinder to do more than tidy your cuts.

Remedies
There are several remedies to relieve the soreness:

Cucumber melon antibacterial hand lotion
Vitamin E.
Tea tree oil
Germolene

Refining Edges

You can make the freshly cut glass safer to handle by gently wiping the edges of the cut piece with the waste piece. This removes the sharpest edges without chipping the glass.

After the glass is scored and broken, you can remove small, unwanted chips with grozing pliers. The serrated jaws of these pliers are used to gently nibble away at the jagged edges.

Rough edges can also be smoothed with a carborundum stone. You rub the stone along each edge, upper and lower, to remove any sharp edges. You can remove more glass with the stone if you wish by a little more aggressive grinding action or just a longer light rubbing of the stone against the edges.

A diamond smoothing pad removes glass in much the same way as a carborundum stone, but does it more quickly with the coarser grades. You can use a number of grades to get an almost bright polish to the edges. These pads must be used with water.

A glass grinder is used by many people. Many models of grinders are available. The grinding surface of the bit is covered with fine diamonds, which grind away unwanted glass very quickly without chipping the edges. In addition, they are water-fed which keeps the glass from cracking due to heat, prolonging the life of the diamond bit, and preventing the powdery ground glass form flying around.

A glass grinder is not a substitute for accurate cutting.

Polishing Solder lines

Before polishing, clean the solder (see cleaning tips) and apply the patina, if any.

Use a good quality furniture polish or wax. Shake the bottle well if it is a liquid, then apply liberally to a soft cloth, or good quality paper towel, rubbing all over solder. If you have a glass with a deep texture, try to avoid this all over process, as it can be hard sometimes to remove all of the polish afterwards, and it is noticeable when it dries. Alternatively, mask off the glass from the solder.

Immediately after applying the polish, take a clean, dry soft cloth or new paper towel, and begin to gently rub the solder seams. If you are using paper towels, you will need a lot of them, as they tear up quickly. When both sides have been polished, check for any missed spots, especially along the edges of your solder seams. Also check for polish residue in tight corners and along the edge of the solder. An old toothbrush often works to remove it. If you need stiffer bristles, make sure you keep this new toothbrush separate from all the others in the house.

Grinding Tips

Protect your cartoonWhen grinding a lot of pieces, you can place a piece of clear float glass over top of your paper pattern, or encase it in plastic to protect it from becoming wet. Then you won't have to grind, dry, test, and repeat. You can just grind and test, quickly grinding where needed.

Placing your cartoonAlso try to have your pattern where you are test fitting right beside your grinder, to cut down on time spent moving from grinder to pattern.

Grinder resevoir maintenanceRinse out your grinder sponge often (at least daily), and replace when it becomes deformed.

Clean out the ground up glass in the bottom of your grinder regularly with a narrow putty knife. Scrape it out into a small old plastic container with a top, and then throw the container into the garbage when it is full.

Grinder head maintenanceMove your grinder head up or down, as it is wears, to a new section. You should be able to get three or four sections out of a typical grinder head.

Finger Cuts while Grinding Glass

Before serious grinding, first run the whole perimeter of the piece very lightly against the grinder. This removes the worst of the 'scalpel' edges and avoids the micro cuts on your fingers.

Let the grinder do the work. Many people seem to put huge pressure on the piece to grind away the waste more quickly, but this is actually counter-productive. Less pressure means less fatigue, less chipping at the edges, fewer broken pieces, and most importantly, fewer cuts to the finger tips.